Water Sorption, Glass Transition, and Microstructures of Refractance Window- and Freeze-Dried Mango (Philippine "Carabao" Var.) Powder

Water sorption isotherms, glass transition, and microstructures of Refractance Window (RW)- and freeze-dried Philippine Carabao mango powders were investigated. Water sorption isotherms were developed by the isopiestic method, while thermal transition of the powders, at various water activities (a(w)=0.11-0.86), was determined using differential scanning calorimetry (DSC). The sorption isotherms of RW- and freeze-dried (FD) mango powders exhibited a type III sigmoidal curve, showing higher and lower adsorption capacities above and below 0.5 a(w), respectively. A significant difference (p<0.05) in water content of RW- and freeze-dried mango powders for equivalent water activities was obtained above 0.5 a(w). The onset glass transition temperature (T-gi) of RW- and freeze-dried mango powder solids decreased as the water content increased. There were no significant differences (p0.05) in T-gi of RW- and freeze-dried mango powder solids at constant water activities, except for a(w)=0.86. Microscopic examination of mango powders indicated that freeze-dried mango powders exhibited greater surface area and porosity in comparison to RW-dried mango powders.